Temperature-dependent sex determination in reptiles While the sex of most snakes and most lizards is determined by sex chromosomes at the time of fertilization, the sex of most turtles and all species of crocodilians is determined by the environment after fertilization.
Sexual Development. For instance, polychlorinated biphenyls PCBs are pollutants whose molecules are structurally similar to some estrogens.
This model indicates that there is no genetic predisposition for the embryo of a temperature-sensitive reptile role of temperature in sex determination in reptiles by mack in Peterborough develop as either male or female, so the early embryo does not have a "sex" until it enters the thermosensitive period of its development.
These chemicals block the conversion of testosterone to estradiol during development so each sex offspring can be produced at all temperatures. One possible explanation that TSD is common in amniotes is phylogenetic inertia — TSD is the ancestral condition in this clade and is simply maintained in extant lineages because it is currently adaptively neutral or nearly so.
PCBs can act as an estrogen replacement, causing feminization of sex organs in growing reptiles. Therein it differentiates into a minute 1—3-mm-long male that is essentially a sperm-producing symbiont of the female see Figure 3.
Bibcode : Natur. Synergism between temperature and hormones has also been identified in these systems. CrewsJ. Bull and D. In crocodilian species—the most studied of which is the American alligator— both low and high temperatures result in females and intermediate temperatures select for males.
Individuals with low levels of aromatase during the thermosensitive period will develop male characteristics.
See Subscription Options Already a subscriber? Vertebrate Life. Reptiles in which both incubation temperature and sex chromosomes interact to determine sex may represent "transitional" evolutionary states between two end points: complete GSD and complete TSD.
See Subscription Options. Evolution and Development.